This invention relates to electromagnetic flowmeters and in particular to such meters in which the electromagnet is energized by direct current pulses.
In an electromagnetic flowmeter a magnetic field across a flow tube generates a voltage in a fluid flowing through the tube. The voltage, which is proportional to flow rate, is sensed by a pair of electrodes in contact with the fluid and amplified by a signal processing system to produce an output signal which is proportional to flow rate.
The magnetic field across the flow tube is generated by an electromagnet excited by a driver circuit. Presently known electromagnetic flowmeters utilize either alternating current or pulsed direct current driver circuits. The advantages and disadvantages of each type of driver circuit are discussed in U.S. Pat. No. 3,783,687, to Mannherz et al, and in U.S. Pat. No. 3,965,738, to Watanabe, for example. Although, as pointed out in these patents, a pulsed direct current drive provides numerous advantages, perturbations (spikes) caused by the rise of current in the magnetic coils and fluctuations in the "steady state" current degrade the accuracy and precision of the meter. Many such meters are also subject to drift with time and changes of temperature.